1. Field of the Invention
The present invention relates to a method of monitoring and controlling traffic in real time in an ATM switching node by controlling the cell transmission rate of various traffic sources having variable bit rates.
2. Description of the Related Art
The ATM (Asynchronous Transfer Mode) network generally requires means for controlling the traffic and bandwidth to effectively transmit information with QOS (Quality Of Service) demanded by the user. The traffic service classes usually provided by the ATM switching system are based on CBR (Constant Bit Rate), RT-VBR (real time-Variable Bit Rate), NRT-VBR (nonreal time-Variable Bit Rate), ABR (Available Bit Rate), UBR (Unspecified Bit Rate), etc. Particularly among these, the VBR service has to be provided in real time as with video signals. Since it needs varieties of bandwidth and shows burst property, the switching node of an ATM network must be provided with means for monitoring and controlling the traffic in order to utilize the network resources over the negotiated traffic parameter. However, if the means for controlling the traffic does not properly work to meet variations of the traffic transmitted over the ATM network, it may cause traffic congestion in the network carrying the VBR traffic.
The GCRA (Generic Cell Rate Algorithm) recommended by the ATM Forum to control the ATM traffic, which is also called xe2x80x98virtual scheduling algorithmxe2x80x99 or xe2x80x98continuous-state leaky bucket algorithmxe2x80x99, is to control the maximum cell transmission rate, cell delay variation, average cell transmission rate and burst allowance. This provides means to control the transmission rate of data cells inputted through the switch by means of limited values of the buffer and increments of the counter determined with traffics. Although GCRA is a simple algorithm with good performance to detect whether the negotiated cell parameter is met, it is not necessary to use this algorithm as UPC (Usage Parameter Control). Instead, any UPC algorithm may be installed provided that QOS may be guaranteed for a call to transmit cells according the negotiated parameter.
Originally, GCRA is proposed as an algorithm to control the cells by detecting violation of the negotiated cell parameter, and gives no rules for the other functions. However, the system designer tends to modify GCRA to monitor the traffic inputted to the switching node in order to measure the rates of using the band by the calls of all the users. In order to control the cell transmission rate, guarantee QOS, and improve the network performance, it is necessary to monitor the traffic transmitted over the network regardless of the ATM service classes. In addition, while it is possible to check the traffic loaded on the network by means of GCRA and the resource management (RM) cell for feedback control, these algorithms are not originally and mainly intended to monitor the traffic, so that the VBR traffic cannot be correctly monitored. Hence, such conventional technologies suffer the following drawbacks when employed to monitor and control the ATM traffic with various characteristics:
1. At least two counters, one for controlling the maximum cell transmission rate and the other for the average cell transmission rate, are required to monitor and control a VBR and VC (Virtual Connection, Virtual Channel, Virtual Circuit).
2. For allotting the network resources to VBR and ABR services are required the buffer size and leaky rate pairs according to the number of the connections. In addition, it is very difficult to uniformly control the network resources for the wideband services with various characteristics.
3. Since the control algorithm for transmitted data cells is executed only at the measurement time interval initially set, it is impossible to measure the real average cell transmission rate. Namely, the accuracy in the cell transmission rate control of GCRA depends on the size of the leaky bucket.
4. While the traffic flowing into the switching node may be controlled by setting the leaky rate, it is impossible to calculate in real time the rate used by all VC""s of the resources. In addition, the leaky rate for a certain connection means continuous allotment of a fixed band to the connection, so that it is hardly expected to achieve the optimum efficiency of using the network resources.
5. The size of the buffer in the switch is increased with the burst characteristic of information, thus increasing hardware. In order to serve traffic with large burst characteristic, it is desirable to employ a system like the conventional FRP (Fast Reservation Protocol), which however does not provide the functions of monitoring and reporting the traffic. Besides, since the input data cell is first processed by the buffer, it is unavoidable to delay the process.
6. There is no suitable congestion control mechanism, because of the delay characteristic inherent in the high speed channel, which is necessary to control the congestion of the ATM network. Namely, the conventional congestion control mechanism checks the occupancy rate of the buffer provided in the switch, or measures RTT (Round Trip Time) by sending a special control cell to the network link in order to detect the congestion of the network. However, such detection is not performed in real time, so that it is difficult to cope with the overhead resulting from delay in processing or transmitting cell in each switch.
7. While GCRA may control the traffics flowing into the switching node in the conventional ATM network by setting the leaky rate and buffer size based on the parameter, it is impossible to actively readjust the traffic control data or allotted bandwidth when there flows into the switching node traffics having bit rates varying with time.
These drawbacks may be summarized as follows:
The conventional traffic control algorithm can hardly achieve the optimum effect of multiple statistics that is the best advantage of the ATM network. Moreover, even if there remains available parts in the network resources, QOS is frequently affected with the linked connection. Such problems are caused by the fact that most of the traffic control algorithms are not executed in real time, and the functions in the traffic control are performed independently with one another.
The following U.S. patents are exemplars of traffic controller: U.S. Pat. No. 5,867,480 to Robert E. Thomas et al. entitled Method And Apparatus For Controlling Congestion In A Network Node; U.S. Pat. No. 5,812,526 to Chung-Ju Chang et al. entitled Traffic Control Mechanism In ATM Communications Network; U.S. Pat. No. 5,737,315 to Haruo Moritomo entitled Traffic Control Device In Private ATM Network; U.S. Pat. No. 5,640,389 to Furnitoshi Masaki et al entitled Traffic Shaper and Packet Communication Apparatus; U.S. Pat. No. 5,581,545 to Haruo Moritomo entitled Traffic Control Device in Private ATM Network; and U.S. Pat. No. 5,519,689 to Young-II Kim entitled Traffic Control Apparatus And Method Of User-Network Interface Of Asynchronous Transfer Mode.
It is an object of the present invention to provide a method for monitoring and controlling traffic in real time in a switching node of an ATM network to guarantee QOS demanded by the user.
It is another object of the present invention to provide a method for controlling the cell transmission rate of VBR traffic flowing into an ATM switching node to optimize the efficiency of using the ATM network resources according to the input state of the traffic.
According to the present invention, a method for monitoring and controlling traffic in real time at an asynchronous transfer mode (ATM) switching node, comprising the steps of retrieving the virtual path identifier (VPI)/virtual channel identifier (VCI) field and cell loss priority (CLP) field from the header of a received ATM cell to determine the validity of the cell by checking the effective value of the header for VPI/VCI field, comparing cell monitoring counter value (Cm) with cell control counter value (Cc) to detect violation of traffic parameter when the cell is determined to be valid, determining whether the present user""s connection violates the negotiated parameter by means of traffic control data (Active_Idle) and CLP when the cell violates the traffic parameter, holding, tagging and discarding the cell according as the cell violates the negotiated parameter, transferring the result of controlling the valid cell to the physical layer to process the cell, and reporting the cell monitoring counter value to a control panel of upper hierarchy to reset the cell counter control value based on the cell monitoring counter value.